Kohler K9J Service Manual page 111

PISTON AND RINGS
Identification
Three different styles of pistons are currently being
used in Kohler K-Series engines.
Style "A" pistons can be used in all K-Series en-
gines. The style A piston can be identified by its
full skirt and its lack of an installation direction
identifier on its crown (a new piston can be in-
stalled facing either direction).
No Installation
D.irecUore ldea,ti,f,ier
The Style "C" piston is used on the K341 engines
only. It can be identified by its partial skirt and
raised criss-cross design in the recessed area
around the piston pin bore. In addition, it has an
installation direction identifier (a notch) at its top.
The style C piston is to be installed with the notch
facing the flywheel.
Installation---.........
Direction
Identifier
(Notch)
Style C Piston
Partial Skirt
with Raised
The Style "D" piston has been used on the K181 ,
K301, and K321 engines. It can be identified by its
partial skirt and rectangular recessed area around
the piston pin bore. In addition, it has an installa-
tion direction identifier, Fly, which is stamped into
the top of the piston. The style D piston is to be
installed with the arrow of the Fly mark pointing
towards the flywheel.
11.8
Installation---..._
Direction
ldenUfier
Style D Piston
Piston Sizes - All Styles
Partial Skirt
with Rectangular
Recess
In order to ensure a correct fit between piston and
cylinder we utilize two cylinder bore sizes at the
factory. Cylinder blocks are honed to the Standard
(STD) size or .003: (.075mm) oversize with corre-
sponding pistons. Blocks using the oversize are
stamped on the cylinder head gasket surface with
. 003". It is essential that . 003" oversize pistons
are used in these blocks to prevent possible fail-
ure such as a noisy engine or eventual piston skirt
cracking. These pistons are available from Kohler.
Standard Service Rings should be used with both
Standard and .003" oversize pistons. Ring end
gap will increase slightly when installed on .003"
oversize pistons; however, sealing is maintained
due to the ring design.
Inspection
Scuffing and scoring of piston and cylinder wall
occur when internal temperatures approach the
melting point of the piston. Temperatures high
enough to do this are created by friction, which is
usually attributed to improper lubrication, and/or
overheating of the engine.
Normally, very little wear takes place in the piston
boss-piston pin area. If the original piston and
connecting rod can be reused after new rings are
installed, the original pin can also be reused but
new piston pin retainers are required. The piston
pin is included as part of the piston assembly - if
the pin boss in piston, or the pin are worn or
damaged, a new piston assembly is required.
Ring failure is usually indicated by excessive oil
consumption and blue exhaust smoke. When rings
fail, oil is allowed to enter the combustion chamber
where it is burned along with the fuel. High oil
consumption can also occur when the piston ring
end gap is incorrect because the ring cannot
properly conform to the cylinder wall under this
condition. Oil control is also lost when ring gaps
are not staggered during installation.
When cylinder temperatures get too high, lacquer
and varnish collect on piston causing rings to stick
which results in rapid wear. A worn ring usually